Just about everybody has seen a rainbow. They are truly one of nature's most lovely natural phenomena. Now imagine a rainbow that occurs at night, lit by the moon rather than the sun. Such things exist, and they are called moonbows. They are very rare, of course, and very difficult to photograph. NASA has a picture here, but it required such a long exposure time that it appears as just another garden-variety rainbow.

I believe they are most often seen under a full moon at the base of waterfalls. Here is one at Cumberland Falls in Kentucky. They've also been spotted at certain falls in Yosemite National Park.

These photos show colors but I've read that there is not enough light by moonlight to see colors and that night rainbows therefore are seen by the human eye as stripes of different shades of gray. Even so I've always wanted to see one.